Antennas

Abstract

An active antenna array is arranged to activate subsets of switchable elements causing the antenna to form a first beam having a first beam pattern, and later to form a second beam having a second beam pattern of substantially identical far field radiation pattern to the first beam pattern but with different origins. A receiver receives radiation reflected from a target back to the antenna when the antenna is configured with the first beam pattern and then when configured with the second beam pattern, and compares the phase of the radiation received at the receiver when the antenna is configured with the first beam pattern with the phase of the radiation received at the receiver when the antenna is configured with the second beam pattern to provide a phase difference signal. A target locating means determines the angular location of the target from the phase difference signal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a national stage of International Application No. PCT / IB2010 / 000277 filed Feb. 11, 2010, the disclosures of which are incorporated herein by reference, and which claimed priority to Great Britain Patent Application No. 0902314.4 filed Feb. 12, 2009, the disclosures of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]This invention relates to improvements in antenna arrays, such as active slot antennas and the like, which can be configured to produce a set of directional far field radiation patterns suitable for use in determining the angular location of a target.[0003]The use of radar to determine the distance to a target is well known. In a very simple system the time of flight of a signal transmitted from an antenna to a target and returning to the antenna provides an indication of the range of the target. This works well for targets that are very far away, but for close targets the time of...

AI Technical Summary

Benefits of technology

[0012]In particular, the invention may be used to achieve the same levels of angular resolution that can be achieved from prior art multi-element arrays from arrays with fewer elements. Alternatively it can be used to enhance the performance of any given multi-element array.

[0023]To enhance the usefulness of the apparatus, it may be arranged to provide multiple pairs of first and second drive signals, each pair of drive signals causing the antenna to be configured in first and second beams patterns, with the shapes of each pair corresponding to identical, but offset, far field radiation patterns. For example, each beam pattern may define a far field pattern having a single major lobe directed in a predetermined direction, with the major lobe of each pair pointing in a different direction to that of any of the others e.g. a set of directional beams covering a range of angles wider than any one of the major lobes.

Problems solved by technology

This works well for targets that are very far away, but for close targets the time of flight may be too short to be analysed.

In the case of automotive applications, for instance, the distance to a target is typically of the order of only a few hundred metres or less, making measurements based on time of flight impractical.

This makes the radar expensive and also bulky as there are constraints on the acceptable spacing between elements.

Since each beam needs to be held in place for a given length of time in order to obtain high quality velocity information, a large number of beams may produce an unacceptably high radar cycle time.

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